The present invention is directed to a collapsible energy absorbing steering column assembly which, upon impact from the occupant-driver, as may occur during a collision of considerable magnitude, allows an added degree of safety to the occupant. It is designed to axially collapse upon receiving an impact load from the occupant of a predetermined magnitude. Such systems are in common use today and may or may not be used in conjunction with an air bag which would inflate instantaneously upon impact and act as a barrier between the occupant and the steering wheel and other vehicle structures within the passenger compartment.
Such systems may include a steering column assembly which is designed to yield within itself, i.e., a "tube-in-tube" construction wherein the steering column and steering shaft are each of two-piece concentrically arranged construction allowing one section to telescopically fold within the other section. Alternatively, the steering column body can be a one-piece construction with the steering shaft itself being designed to yield, such as by bending. The steering shaft may be of one-piece construction from the steering wheel to the steering gear box, or it may be of multiple piece construction with U-joints in between the separate pieces.
Examples of such systems include the tube-in-tube steering column assembly shown in U.S. Pat. No. 3,415,140 wherein it is noted that the collapsible steering column body and internal steering column assembly is secured to a support structure by means of a support bracket which is held to the support structure solely by means of a frictional clamping arrangement. Once the friction of the fastening means is overcome by the impact load, the collapsible steering column assembly is released from all clamping engagement with the support structure. No means is provided for accommodating the possibility of vertical displacement of the steering wheel and absorbing the energy of any vertical displacement in a controlled manner. Further, because of the uncertainties provided in a pure friction clamping arrangement, the point at which the steering column assembly will be released from the support structure may vary over a fairly wide range of impact loads, and it will vary at each point of securement.
U.S. Pat. No. 4,098,141 is directed to the same type of system as shown in U.S. Pat. No. 3,415,140 but, by provision of a Teflon washer between the support bracket and support structure, seeks to eliminate the variance of any frictional clamping inconsistencies. Upon release, the collapse of one steering tube within the other is controlled by metal deformation upon the initial release of shear pins holding the two tube sections fixed to one another.
Other systems exist wherein the energy absorbing characteristics of the system are designed solely within the support bracket itself with the energy absorption capabilities being a combination of friction and metal deformation such as shown in U.S. Pat. No. 4,838,576 or pure metal deformation as shown in U.S. Pat. No. 4,703,669. In the latter disclosure, the support bracket allows for vertical displacement and energy absorption in the generally vertical direction.
Finally, there is that general class of collapsible energy absorbing steering column assemblies wherein the energy absorption characteristics are included in the mounting bracket, either solely or primarily, which secures the steering column body to the vehicle support structure and which includes (i) impeding the collapse of the steering column assembly by the bolt torque friction created between the mounting bolt securing the support bracket to the support structure, and (ii) controlled, or at least semi-controlled, deformation of the mounting bracket itself. Disclosures showing such systems are seen in U.S. Pat. Nos. 4,194,411; 4,022,495; 4,228,695; and 4,786,076.
In certain instances, the mounting bolts also serve as guide pins for guiding the axial collapse of the steering column assembly, such as shown in U.S. Pat. Nos. 4,022,495; 4,228,695; and 4,786,076. Further, in aforementioned U.S. Pat. Nos. 4,228,695 and 4,194,411, the mounting bracket is seen to accommodate vertical displacement of the steering wheel as well as axial displacement.
However, in none of the aforementioned systems is there provided a collapsible energy absorbing steering column assembly wherein the mounting bolt torque friction is completely eliminated from the function of absorbing energy upon axial displacement or throughout the entire axial displacement of the steering column assembly.
Further, none of the prior art systems provide a simple and economically designed support bracket providing: (i) a reliable guide for controlling axial displacement by pure bending deformation, (ii) eliminating lateral displacement and the uncertainties it causes in the controlled energy absorbing axial displacement of the steering column assembly, and (iii) permitting a limited degree of vertical displacement of the steering wheel assembly while absorbing the impact energy of such a vertical displacement.
The system shown in U.S. Pat. No. 4,000,876 is an example of an energy absorbing steering column support bracket providing for axial displacement of the steering column assembly without first having to overcome any frictional forces caused by positive torque mounting. On the other hand, the system does not include any positive torque mounting of any kind and, because of its being mounted within a pair of resilient sleeves, it is subject to constant floating and passing vibrations from the vehicle suspension through to the driver's hands.